1. Field of the Invention
This invention relates to a semiconductor laser (laser diode) for obtaining radiation having a relatively short wavelength in comparison with the usual wavelengths of semiconductor lasers.
2. Description of the Prior Art
In fact, of the conventional semiconductor laser diodes known to the inventors, the shortest wavelength obtained with semiconductor laser diodes is of the order of 0.8 micron and is therefore located in the infrared region. In contrast, the invention makes it possible to attain the visible light region, thus offering the following advantages:
(1) the possibility of visual control; PA1 (2) enhanced resolution of optical systems and especially readers for videodisks, audiodisks and optical disks insofar as the resolution is limited by the diffraction phenomenon. PA1 either to reduce the wavelength, which is the object of the present invention; PA1 or to increse the numerical aperture, thus producing an increase in aberrations which are proportional to the fourth power of U, thus giving rise to a disadvantage in that it is necessary to correct these aberrations by means of highly efficient and therefore very costly optical systems.
In these applications, the laser radiation is focused on the surface of the disk. The radius of the focal spot is given as a function of the wavelength and of the numerical aperture (sin U) by the formula: EQU R=(0.61.lambda.)/(sin U)
In order to increase the resolution, it is necessary to reduce R and therefore:
In consequence, it is clearly an advantage to give preference to a reduction in the wavelength emitted by the semiconductor laser.